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imgix and Third-Party CDNs

imgix combines sophisticated image manipulation, our proprietary caching infrastructure, and the performance improvements of an industry-leading CDN (content delivery network) into a powerful end-to-end service. Our integrated solution gives us full visibility and flexibility over the entire image pipeline, making the service robust and easy to integrate.

With our global delivery network, your images will get to your users quickly no matter where they are. No additional CDN is required to cache them and provide a great experience to your end users.

If at all possible, we recommend that you not use a third-party CDN on top of the one we provide. Due to the close integration of all components of the imgix service, performance with a third-party CDN may be reduced and some features will not be available.

Effects on Speed and Cache Hit Ratios

Having two CDNs participate in each image request will cause initial image renders to take longer, and will have adverse effects on cache hit ratio. Cache hit ratio is the percentage of requests served by the CDN cache versus requests that have to go back to the origin. Adding a third-party CDN increases the chances of an initial miss, because it will not be tuned to match up to our backend systems in the way our CDN is.

Diagram describing impact to hit ratios of adding a third-party CDN

imgix-Specific Feature Impacts

In addition to the speed hit and greater chance of cache misses with a third-party CDN, the advanced imgix features listed below rely on our integration of optimization logic at the edge caches, and are therefore not available when using a third-party CDN in conjunction with imgix.

Automatic Content Negotiation

The imgix Automatic Content Negotiation technology is a convenient way to serve more modern image formats to end users based on their device and browser with no additional programming required. We do all of the heavy lifting of evaluating whether the client supports advanced image formats (WebP, JPEG XR, etc.) up front at our CDN, to convert as necessary to the best-optimized format for that client on the fly.

Client Hints Support

Similarly, our support for Client Hints requires our caching logic so it can direct the server to send the best-sized image to a client or browser based on extra information included in the HTTP request headers. Other CDNs don’t provide the logic required to make these features performant, so we are only able to offer them to customers that use the imgix CDN.

Purging

imgix’s CDN purges based on a master image and all of its derivatives, and purges with imgix complete worldwide in less than 1 second on average. In addition, it intelligently purges based on defined relationships between images; for example, if you purge an image that’s being used as a watermark, any images watermarked with that image will also be purged.

SSL with Custom Domains

imgix offers SSL/TLS by default on all of our standard hostnames (*.imgix.net), and when using our CDN. If you do choose to use a third-party CDN in addition to imgix, you will need to work with that CDN provider to get a certificate for the custom domain you desire, and then point that CDN origin to your source’s imgix.net hostname.